The present invention relates generally to an optical disk system. More particularly, the invention relates to a head drive system for performing seek movement of each of a plurality of head for erasing information from, recording information on and/or reproducing information from an optical disk such as magnet optical disk.
In an exemplary optical disk apparatus using an erasable optical disk such as magnet optical disk, a head for erasing information from, recording information on and/or reproducing information from the optical disk is driven by a head drive motor for its seek movement. Generally, drive force is applied to the head in the form of a triangular pattern. Namely, the head is first accelerated at a constant acceleration .alpha. and then decelerated a the constant acceleration .alpha.. For this purpose, eclectic current i is supplied from a source to the drive motor through a power amplifier under fixed voltage V.
In this case, when the weight of the head is given as m, the drive force F for moving the head is represented as F=m .alpha.. Since the acceleration .alpha. is in proportion to the current i, the drive force F is also in proportion to the current i. Further, since the voltage V is fixed, an electric power P required to drive the head is represented as P=Vi.
Recently, an optical disk system which can perform erasure, record or reproduction of information by using a plurality of heads has been proposed. In this kind of optical disk system, it is easy to simultaneously drive all the heads. However, in this case, an extremely large power will be required. In many cases, the system is designed to have an upper limit of a maximum power consumption. Accordingly, when all the heads are simultaneously driven, the power consumption required to drive the heads is apt to exceed a maximum power consumption, resulting in a breakdown of the system.
On the other hand, when the heads are successively driven in such a manner that after seek movement of one of the heads has been completed, seek movement of the next head is started, a power consumption required to drive the heads can be decreased. However, in this case, when seek distance is relatively long, an overall seek time required to complete all the seek movements of the heads will exceed a permissible time-lag between information recording/reproducing operations effected by the separated heads.